Ink jet drop on demand printers are available in two main types, thermal ink jet printers and piezoelectric ink jet printers. The printheads for such printers may be configured as roof-shooters or side-shooters depending on the orientation of the nozzle holes with respect to the actuation devices which cause ink to be ejected through the nozzle holes. Thermal ink jet printers rely on resistive heating elements to heat ink and cause formation of a vapor bubble in an ink chamber adjacent the heating element which urges ink through an orifice toward the print media at an extremely rapid rate. High pressures generated in the ink chamber during the bubble formation and collapse can damage the heating elements during the life of the printhead. Accordingly, ink jet heater chips containing the heating elements as the ink ejection devices are typically fabricated with multiple layers of passivation and protection materials on the resistive heating elements.
As the speed of ink jet printers increases, the frequency of ink ejection by individual heating elements also increases thereby increasing the frequency of mechanical shock experienced by the heating elements. Increasing the thickness or number of protection material layers on the heating elements can increase the life of the printhead, however, the thermal efficiency of the heating elements suffers as the thickness or number of protection layers over the heating element increases. A need exists for ink jet heater chips having increased thermal efficiency and processes for making the heater chips which do not significantly increase printhead fabrication costs.